1. Field of the Invention
This invention generally relates to a snap-apart housing for an interface arrangement for making an apparatus for electro-optically reading indicia having parts of different light reflectivity, for example, bar code or matrix array symbols, compatible with different devices, such as host processors, transaction systems, transaction terminals, video cassette recorders, facsimile machines, video cameras, television boxes and like electronic devices, having data processors which operate with different data exchange formats.
2. Description of the Related Art
Various optical readers and optical scanning systems have been developed heretofore for reading indicia such as bar code symbols appearing on a label or on the surface of an article. The bar code symbol itself is a coded pattern of indicia comprised of a series of bars of various widths spaced apart from one another to bound spaces of various widths, the bars and spaces having different light reflecting characteristics. The readers in scanning systems electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumeric characters that are intended to be descriptive of the article or some characteristic thereof. Such characteristics are typically represented in digital form and utilized as an input to a data processing system for applications in point-of-sale processing, inventory control and the like.
Scanning systems of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,369,361; 4,387,297; 4,409,470; 4,760,248; 4,896,026, all of which have been assigned to the same assignee as the instant application. As disclosed in some of the above patents, one embodiment of such a scanning system resides, inter alia, in a hand-held, portable laser scanning device supported by a user, which is configured to allow the user to aim the scanning head of the device, and more particularly, a light beam, at a targeted symbol to be read.
The bar code symbols are formed from bars or elements typically rectangular in shape with a variety of possible widths. The specific arrangement of elements defines the character represented according to a set of rules and definitions specified by the code or "symbology" used. The relative size of the bars and spaces is determined by the type of coding used as is the actual size of the bars and spaces. The number of characters (represented by the bar code symbol) is referred to as the density of the symbol. To encode the desired sequence of the characters, a collection of element arrangements are concatenated together to form the complete bar code symbol, with each character of the message being represented by its own corresponding group of elements. In some symbologies, a unique "start" and "stop" character is used to indicate when the bar code begins and ends. A number of different bar code symbologies exist, these symbologies including UPC/EAN, Code 39, Code 128, Codeabar, and Interleaved 2 of 5, etc.
In the laser beam scanning systems known in the art, the laser light beam is directed by a lens or other optical components along the light path toward a target that includes a bar code symbol on a surface of the target. A moving-beam scanner operates by repetitively scanning the light beam in a line or series of lines across the symbol by means of motion of a scanning component, such as the light source itself or a mirror disposed in the path of the light beam. The scanning component may either sweep the beam spot across the symbol and trace a scan line across the pattern of the symbol, or scan the field of view of the scanner, or do both.
Bar code reading systems also include a sensor or photodetector which detects light reflected or scattered from the symbol. The photodetector or sensor is positioned in the scanner in an optical path so that it has a field of view which ensures the capture of a portion of the light which is reflected or scattered off the symbol. The captured light is detected and converted into an electrical signal. Electronic circuitry and software decode the electrical signal into a digital representation of the data represented by the symbol that has been scanned. For example, the analog electrical signal generated by the photodetector is converted by a digitizer into a pulse width modulated digitized signal, with the widths corresponding to the physical widths of the bars and spaces. Such a digitized signal is then decoded, based on the specific symbology used by the symbol, into a binary representation of the data encoded in the symbol, and subsequently to the alphanumeric characters so represented.
The decoding process of known bar code reading systems usually works in the following way. The decoder receives the pulse width modulated digitized signal from the digitizer, and an algorithm, implemented in the software, attempts to decode the scan. If the start and stop characters and the characters between them in the scan were decoded successfully and completely, the decoding process terminates and an indicator of a successful read (such as a green light and/or an audible beep) is provided to the user. Otherwise, the decoder receives the next scan, performs another decode attempt on that scan, and so on, until a completely decoded scan is achieved or no more scans are available. Such a signal is then decoded according to the specific symbology into a binary representation of the data encoded in the symbol, and to the alphanumeric characters so represented.
Moving-beam laser scanners are not the only type of optical instrument capable of reading bar cede symbols. Another type of bar code reader is one which incorporates detectors based on charge coupled device (CCD) technology. In such readers the size of the detector is typically smaller than the symbol to be read because of the image reduction by the objective lens in front of the CCD. The entire symbol is flooded with light from a light source such as light emitting diodes (LED) in the scanning device, and each CCD cell is sequentially read out to determine the presence of a bar or a space.
The interfacing of scanning heads with host devices having data processors utilizes arrangements such as described in U.S. Pat. No. 5,258,604. In such prior art arrangements, the interface arrangement has circuitry for storing and applying an identification code representing the identity of a selected one of a plurality of input/output (I/O) devices to the decoder of the scanner, for operating the decoder, and for transferring decoded signals and command signals between the selected one of the I/O devices and the decoder.